Moore tornado images

The deadly tornado that swept through the Oklahoma suburb of Moore has now been upgraded to an EF-5 on the Enhanced Fujita scale by the National Weather Service. The breadth and severity of the damage caused suggest that the wind speeds must have been in excess of 337kph.

At some points along its path of 27km, the storm was almost 3km wide. Large tornadoes are usually nearer 500 to 900m in width. The storm was believed to have been on the ground for around 40 minutes.

Debris from the storm has been found up to 160 km away. Less than one percent of all US tornadoes are this violent. That amounts to about 10 a year.

In most cases they track across the vast open plains known as Tornado Alley and do not affect major conurbations. That was the case with the massive storm of 1999. On that occasion the storm followed a similar track to the latest twister, but crucially on that occasion, it veered to the north, just before reaching the centre of Moore.

The winds recorded in the 1999 storm were estimated by Doppler radar to be up to 486kph, the highest winds ever recorded on Earth. Average speeds of this recent tornado suggest that it was travelling at around 35kph. Violent tornadoes, typically move at much more quickly than that and can reach speeds in excess of 100kph.

Initial reports placed the death toll as high as 91 people. Thankfully that number was later lowered to 24 at the time of writing, and the search for survivors continues.

The relatively low death toll may have been down to the improved warning system. Residents were given around 16 minute’s notice ahead of the storm’s arrival. That may not sound like much but 20 or 30 years ago, that number was nearer three to five minutes.